Laser scanning cytometry (“LSC”) is a well established analysis tool that can be used to determine various characteristics of cells. U.S. Pat. No. 4,647,531, hereby incorporated herein by reference, provides a generalized cytometry instrument which includes translocating means which provides electromechanical forces capable of moving a surface upon which live cells are immobilized. The translocating means may alternatively move a cell locating means, illuminating means and detecting means over a stationary surface to produce a representation or graphical illustration of cell numbers and responses.
Some LSC systems utilize a blocker bar configured to prevent a beam of light from striking a detector when a cell is not present between the source of the beam and the detector. Such a configuration, however, allows forward scattered light to strike the detector when the beam strikes a cell before impinging on the blocker bar. The capture of forward scattered light by the detector enables the creation of a dark field image with an undefined bright field representing the cells (i.e., contrast-field image).
U.S. Pat. No. 6,002,788 ('788 patent), also hereby incorporated by reference herein, provides a method and device for creating visual images of cells using LSC by modifying a blocker bar to be configured such that a portion of a beam of light strikes a detector when a cell is not present between the source of the beam and the detector. When the beam impinges on a cell, however, a portion of the forward scattered light impinges on the detector creating an additional signal while another portion of the forward scattered light is negatively scattered. The contrast of detected scattered light permits the detector to create signals capable of creating a visual image of the cell.
The use of a blocker bar in LSC requires the manipulation of an additional element that complicates the design of such devices. In addition, a blocker bar may require specific manufacturing to optimize visual imaging, as taught by the '788 patent, or the contrast-field imaging presented in earlier LSC devices. Thus, an advantage may be accrued by eliminating the use of a blocker bar.